The present invention relates to a process for preparing silicon carbide powder from a vaporized polysiloxane. This process is unique in that the polysiloxane is reacted and pyrolyzed to form the SiC powder in a single step. The silicon carbide powder produced by this process, moreover, is desirable in that it is non-agglomerated and, thus, can be densified to form silicon carbide bodies.
Silicon carbide ceramics have found utility in numerous applications because of their desirable properties and characteristics. The production of such ceramics, however, requires silicon carbide powder which is inexpensive, pure and in a form which can be easily sintered to the desired ceramic.
Silicon carbide powder can be produced by a number of known techniques using a variety of silicon containing compounds. For example, SiC can be formed by vapor phase pyrolysis of organosilicon compounds such as alkylated silanes (see e.g., Canadian Patent No. 592,456); mixtures of silicon halides and hydrocarbon gases (see e.g., U.S. Pat. Nos. 3,346,338 and 4,295,890); and polysilanes (see e.g., 4,676,966 and 4,571,331). Similarly, silicon carbide can be formed by the reaction of silica and carbon or by the pyrolysis of a variety of non-vapor phase organosilicon polymers such as polysiloxanes (see e.g., U.S. Pat. No. 4,840,781); polycarbosilanes (see e.g., U.S. Pat. No. 4,465,647); and polysilanes (see e.g., 4,534,948). What is not taught in these references, however, is the use of vaporized polysiloxanes for forming the SiC powder.
Suzuki et al. in U.S. Pat. No. 4,613,490 teach a process for forming SiC powder in which a polysiloxane undergoes a vapor phase reaction to form an SiCO product at a temperature less than 1600.degree. C. which is then heated (calcined) to form the resultant powder. As is evident, this process is time consuming and expensive because it requires a second heat (calcining) step to form the powder. In addition, the powder prepared by this 2 step process is often highly agglomerated and is difficult to densify.
The present application discloses for the first time that silicon carbide powder can be produced from vaporized polysiloxanes in a process with only a single heating step.